That works.
Thanks for your kind support.

/usr/local/bin/gpg-agent -v --daemon

gpg-agent[2676]: listening on socket '/home/nui/.gnupg/S.gpg-agent'
/usr/local/bin/gpg-agent: relocation error: /usr/local/bin/gpg-agent: symbol
assuan_sock_set_flag, version LIBASSUAN_1.0 not defined in file libassuan.so.0
with link time reference

Yes, with exit code = 127

gpg-connect-agent -v

gpg-connect-agent: no running gpg-agent - starting '/usr/local/bin/gpg-agent'
gpg-connect-agent: waiting for the agent to come up ... (5s)
gpg-connect-agent: waiting for the agent to come up ... (4s)
gpg-connect-agent: waiting for the agent to come up ... (3s)
gpg-connect-agent: waiting for the agent to come up ... (2s)
gpg-connect-agent: waiting for the agent to come up ... (1s)
gpg-connect-agent: can't connect to the agent: IPC connect call failed
gpg-connect-agent: error sending standard options: No agent running

Thanks. I'm very happy with gnupg 2.1.

Which version of Libgcrypt are you using. (gpg --version shows it)

libgcrypt-config --version
1.6.4

When did you create your GPG key of ed25519?
Or... did you register your SSH key by ssh-add?

The ssh key was generated by "ssh-keygen -t ed25519" and added by ssh-add.

If you can binary-edit, please add
prefix @ (0x40) to the public key in the *.key file.

I change from:

(3:ecc(5:curve7:Ed25519)(5:flags5:eddsa)(1:q32:..

to:

  (3:ecc(5:curve7:Ed25519)(5:flags5:eddsa)(1:q33@:..

then 'ssh-add -L', and get
The agent has no identities.

It seems not working for me. By the way, I switch to 2.1.7 version which
doesn't have this problem.